Review the rules

Air Safety Week, Dec 6, 2004

Martin Aubury, former head of aircraft structures at Australia's Civil Aviation Authority (now the Civil Aviation Safety Authority, CASA) offered a few thoughts now that the investigation into the 2001 crash of American Airlines Flight 587 has been wrapped up (see ASW, Nov. 1). Aubury is among those who think it "unfair to blame the pilot." Aubury raises his sights and looks to the regulations:

"Fault lies more with a design rule that is 50 years out of date and no longer reflects reality. When the 'Yaw Maneuver Condition' was conceived, there was little likelihood of rapid rudder pedal reversals because pedal loads were far too high. Likewise, prior to power assistance, pilots would have found it physically difficult to apply maximum rudder in combination with significant aileron or elevator.

"Now it's all too easy to apply repetitive control inputs and/or combined input, neither of which are envisaged by the design rules - and either of which can break the airplane.

"Nor do I retreat from an earlier observation that irrespective of what caused the Flight 587 crash, the Federal Aviation Administration should review the rules for flight into continuous turbulence. The regulation, FAR 25 Appendix G, is based on statistical representation of atmospheric turbulence that predates wake turbulence from widebody aircraft. So there is a greater risk of encountering an overload condition than is postulated by the certification standard, because it does not allow for wake turbulence.

"I still ponder if the fin would have failed had it been metal. One of the notable drawbacks of composite structures is that they do not deform plastically in the range between limit load and ultimate load, so there is little redistribution/alleviation of loads. Think of the many cases where oldfashioned metal aircraft have crept home with severe tail damage. Even Concorde lost pieces of its rudder on four occasions without serious damage to the rest of the tail."

>> Aubury, e-mail ozaubury@homemail.com.au <<

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